Secondary graviton spectra and waterfall-like fields

TL;DR

This paper calculates the secondary gravitational wave spectra caused by waterfall-like fields, establishing constraints on their properties and comparing them with primary spectra and observational bounds from LIGO/Virgo and space interferometers.

Contribution

It provides explicit bounds on waterfall field spectra and compares secondary graviton signals with primary spectra and observational limits.

Findings

Derived bounds on waterfall spectrum amplitude and slope.

Compared secondary spectra with primary gravitational wave backgrounds.

Assessed detectability prospects with space-borne interferometers.

Abstract

The secondary spectra of the gravitons induced by a waterfall-like field are computed and the general bounds on the spectral energy density of the tensor modes of the geometry are translated into explicit constraints on the amplitude and slope of the waterfall spectrum. The obtained results are compared with the primary gravitational wave spectra of the concordance model and of its neighboring extensions as well as with the direct Ligo/Virgo bounds on stochastic backgrounds of relic gravitons. Space-borne interferometers (such as Lisa, Bbo, Decigo) seem to be less relevant but their potential implications are briefly outlined.